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'                            72                PRACTICAL ORGANIC CHEMISTRY

I                           crystalline oxime separates.    The presence of any free hydroxyl-

\                         amine is then tested in a few drops of the liquid with Fehling's

solution, or by merely adding a drop or two of copper sulphate,
r                          then a sufficient quantity of caustic soda to produce a clear blue

solution and warming.   An orange-red precipitate of cuprous
! |                         oxide   indicates   uncombined   hydroxylamine.      If   no    free

hydroxylamine is present, the liquid is shaken up with an equal
•*i                         volume of ether,   in   which   the   acetoxime   dissolves.     The

«                           ethereal solution is separated and the process repeated twice

1                         with fresh ether.     The united ethereal extract  is  filtered,   if

j                        necessary, through a dry filter into a distilling   flask.    The

|                        greater part of the ether is distilled off on the water-bath.    The

!                        remaining liquid is poured into a glass basin and the rest of the

ether left to evaporate in the air, the last traces being removed
by heating for a few minutes on the water-bath.    The acetoxime
i<*                         separates out on cooling in colourless needles.     It is dried ori

I                        a porous plate and recrystallised from a little petroleum spirit

' ||                        m. p. 61—62.°   Yield 4—5 grams.

,1                                     CH3. CO.CH3 + NH2OH.HC1 4- NaOH

fl                                                   =CH3.C:NOH.CH3 + NaCl + 2H2O

i!                           Properties.—Colourless needles ; m. p. 60°.

fj                           Reaction.—Boil a small quantity for a few minutes with dilute

hydrochloric acid, and test with Fehling's solution. The oxime
is decomposed into acetone and hydroxylamine,

CH3.C(NOH).CH3+ H2O = CH3.CO.CH3 + NH3OH.
Melting-point Determination.—For this purpose the
following apparatus is used (Fig. 53).   A small sample of finely
powdered substance, which has been carefully dried, is introduced
into a capillary tube of about i mm. inside diameter sealed at
|§                   one end.    The tube is made from soft thin-walled glass tubing,

about 15 mm. diameter, by rotating it in the blow-pipe flame until
,   the glass softens, and then quickly drawing it out.     The long
I "'^ i                         capillary is then broken into lengths of about 7 cm. (2^ in.) by

§ j      , '                    scratching across with a writing diamond, and each short tube

is sealed at one end. To introduce the substance, it is con-
venient to scoop up the finely powdered material off a watch
glass with the open end. By tapping the closed end on
the bench, the powder is shaken down. The quantity intro-
duced should occupy a length of about 2—3 mm. when tightly